It is generally agreed that selenium is an essential trace element in livestock, such as poultry and swine, feeds. This is especially true in the case of feeds for young growing animals. While the element occurs naturally in most feed ingredients, its level in feeds such as cereal grains and soybeans is in most areas inadequate to meet the nutritional needs of livestock. Tests have shown that animals absorb dietary selenium according to bodily need and excrete any excess. However, because of the extremely low level at which selenium is to be added to feeds, the nutritional needs of the animals will be satisfied without causing any significant increase in selenium concentration in edible tissues or in the environment. Toxicologists in Canada and the United States have thoroughly evaluated all available scientific data and have concluded that in the amount permitted in feeds for livestock selenium would not constitute a hazard. On the contrary, it is considered that its use is more likely to have a beneficial effect on human health for the same reason that it improves the health of livestock.
However, like other essential trace elements, selenium is extremely toxic if consumed in excessive amounts. It will be readily appreciated therefore that such supplements must be more or less completely homogeneous, i.e., the small percentage of selenium must be distributed uniformly throughout the supplement. Indeed, feed manufacturers wishing to mix feeds, including premixes, containing added selenium may only do so provided the manufacturer can demonstrate competence in his ability to produce batches of selenium-containing supplement which have been proven to be homogeneous by the analysis of three samples taken at random from the batch.
Alternatively, micro-premix feeds containing added selenium and intended for sale to persons who are not required to demonstrate competence in mixing, such as the individual farmer, must be so formulated that not less than 10 pounds of the premix is required to be mixed per ton of complete feed. This added precaution is necessary because of the extremely small amounts of selenium in a feed and the absolute necessity for uniform distribution.
Prior art selenium-containing supplements utilize ground limestone as a carrier for the selenium components. However, with these materials it has proved impossible to obtain a product having a selenium content variability within acceptable limits. For example, a prior art supplement of this type containing 40 p.p.m. selenium typically has a coefficient of variation in the selenium content of 36% and a 20 p.p.m. supplement typically has a coefficient of variation of approximately 80%. Such variations in selenium content are not acceptable in practice when one considers the toxic nature of selenium.
It is an object of the present invention to provide an animal feed supplement having a low selenium content, the supplement being substantially homogeneous as regards distribution of the selenium content.
It is a further object of the present invention to provide a process for producing such a novel feed supplement.